Control of an automatic signalling system



April 10, 1956 R QBERMAN 2,741,665

CONTROL OF AN AUTOMATIC SIGNALLING SYSTEM Filed Nov. 12, 1952 12 Sheets-Sheet 1 LINE LINK FRAME I Q l I Q I fig.1 fig.1a

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April 10, 1956 R. M. M. OBERMAN 2,741,665

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M W M ofl W R United States Patent 'ice 2,741,665 CONTROL or AN AUTOMATIC SIGNALLING SYSTEM Roelof Mam-ten Marie Oberman, The :Hague, Netherlands, assignorto DeStaat der N'ederlanden, Ten Deze Yertegenwoordigd Door de Direceur=Genemal dcr Pesterijen, .Telegrafie en Telefonie, The Hague; Nethensues Application November 12, 1952, No. 319,963

Claims priority, application Netherlands November 12, 1951 28 Claims. (Cl. 179 -18) p The invention relates to the control of an automatic signalling system such as in an automatic telephone or telegraph system, in which the connections in one exchange are established under the control "devices which test the links between the successi-ye selecfing stages in a ay-path outside these selecting stages. 1

Such systems are known with crossbar selector-s: The Bell Laboratofies Record, vol. 17, contains a iiur'nher of extensive descriptions of the crossbar system eeye'loped in the Bell Telephone Laboratories which was called No. l Crossbar System later on. Ont of this system the No. 5 Crossbar System has been developed. the switching stages in these systems are positioned under vthe control of markers, which are only provided very small numbers and of which :only one can work at a time. .In order to avoid this difiicu'l-ty L M. ,Ericsson '(Ericsso'n Review 1950, No. 4), as well as the Swedish Telegraph and Telephone Administration (Tel 1950, No. .2), have developed systems that are builton the old idea that group selectors and fina'l selectors contain only markers which :serve a -:definite selecting stage or part of it, thereby reducing the risk of large derangements caused by the breakdown of a marker.

As has been described in the @berrnan copending U. S. patent application No. 316,574, there are seasiderahle advantages in not building up the trunking diagrams of systems as those described therein according to the conventional arrangement. By the application of the invention such systems can be provided with a number of markers which work practically indepcndently from each other and which only determine the routing of the calls through the exchange; after which such a marker seizes the control circuits individually associated with a limited group of switching devices as well as with the designated route, in order to enable these circuits to set the switches. In order to keep the effect of a contingent fault restricted to the smallest possible vportion of the exchange, the switches-serving a group of associated links should be combined in one control circuit, which means that, if crossbar switches are used, the 11th switch or bridge of each group serving a specified group of subscribers and belonging to the same group of secondary switches in the line-linkirarne,

should be combined in one or more crossbar switches,

Figs. 3, 3a, 3b and Y30 show an example of the trunkirig diagram of an exchange in a six-digit system;

to Pjigsl l and 1a is as follows. is'conne'cted to a sender or register REG, ten of which 2,741,655 .liatented Apr. 110, 1956 Fig. 4 shows :the correlation between the arrange ments according to Figs. 2 and 3;

Fig.- 5 shows the principle of the markers and of the switch control devices as required in the trunking diagram according to Figs. 2 and 2a;

Figs. 6 and 6a show .a diagram similar to Fig. 5 for a 5 or 6 digit system.

The-diagram of Figs. 1 and 1a is given as a first example and only illustrates the general principle. It

a general ,trunking diagram of an exchange comprising a maximum of 9000'numbers in .a iour-digitsys- .tem.-having an outlet via the 0. The diagram is only built npwof line-link frames. The primary switches all consist .e; .g. of 50 Vertical units having ten outlets, as is the case .with the crossbar switch of the American type. With these switches a decimal system can he obtained. The .iifty subscriber's connected to each of them have 10 outlets for the outgoing and incoming trafiic together (.12 (blocking probability) =0.0-1, 3.1 T. U. '(traific units)), which in most cases seems amply sufdci'rit. Twenty of these groups of 50 subscribers are sjyst'einatically distributed over a group of secondary switches of the line-link frame, which groups of secondary switches is divided into two parts, one for the outgoing and the other for the incoming Iraific oi'tlie subscribr'sljlines. For each group of 1000 subscribers there are 1Q groups of secondary switches, each group containing '10 switches "for outgdingand 10 for incoming trafiic. Each switch has 20 outlets, thus occupying 2 vertical units of an Americancro's sha'r switch. rn-ere are '9 or these groups of 0 subscribers, a 16th link frame being destined to trunk lines out-going and incoming via 0. So each group of 1000 subs'c'ribers disposes of 100 connecting circuits. The group of incoming lines also corresponds with agroup of a maximum of I00 connecting circuits. The outgoing terminals or" these circuits are distributed 'by additional links, namely said connecting circuits regularly over the inlet of the secondary incoming switches or the linelink-frame. Each group of these incoming secondary "switches of the line=link frame has been through connected to a group of secondary switches handling the outgoing t-rafiic. The connecting line links shown in Fig. 1 between the incoming secondary switches and the primary switches of this frame are the same as those shown inFig. 1a between :theprimary switches and the outgoing secondary switches i. e. the line link frame inFig. .1 is the same frame as the line link frame in Fig. 1a.

The regular distribution of the right hand terminals of the connecting circuits over the incoming secondary switches "implies that in each group of ten connecting circuits each circuit is connected to different group of switches having access to a certain thousand, so that or the 100 connecting circuits destined to each thousand, "ten are connected to the incoming switches of each other thousand.

So the situation on the secondary switches of a linelink-frame is as follows: On one side 20 groups of 10 links are connected to the primary switches PR'IM, and on the other side these primary selectors are confi ec'tedto the outgoing and the incoming terminals of ihe'connecting circuits, which in their turns are subdivided into 2X10 groups, each comprising 1'0 connecting circuits. 7 1

lf princile the functioning of the system according A calling subscriber base e; g. been provided per 1000 subscribers, one for eaclig'roup of 10X 10 or 100. 1f desiredth'is numherr nay berated higher or lower. The sendersare connected to the secondary switches SEC of the line-link-frame. If required further concentration stages may be inserted.

' the primary switches of'the line-link frame will have positions.

- entrees After the four digits of the required subscribers number la (See Figs. or 6 and 6a), is seized, which seizes three free and mutually connectable links, and completes the required call, i. e. links between it and the calling, the called and their connecting circuits.

Each subscriber can always be connected to any other subscriber via different routes. In this manner an automatic exchange arranged according to the trunking diagram of Figs. 1 and la would have to be equipped with 900 connecting circuits plus a maximum of e. g..90

"incoming connecting or trunk circuits, Whereas, if the connecting circuits could be considered as a full availability group, only about 400 would be required for the trafiic considered.

7 Consequently, for an exchange of 10,000 subscribers equipped with'crossbar switches the trunking diagram'of Figs. 1 and la requires a minimum quantity of switching apparatus at the price of relatively large number of con- Fnectin g circuits, which presents the question whether it would not 'bepossible to reduce the number. of connecting circuits.

Before going into this question, attention should be drawn to the fact that in the diagram of Figs. 1 and la a numerical selection is actually already made before the four digits determine the number 'in the relevant te V have been dialled, a marker, not shown in Figs. 1 and connection of the circuit, i. e. by the selection of the secondary concentration switch and the connecting circuit over which the connection will be established.

It is possible to reduce the number of connecting circuits by combining the connectingcircuits into larger groups, so that the smaller splitting up in consequence of the numerical division of the connecting circuits will result in larger groups. Y

In principle it is possible to combine two IOOO-groups into one 2000-group. Then the secondary switches in the I dine-link frame will have 40 positions, and there Will be 4 /zsuch groups of 2000 subscribers. group of 200 subscribers has 40 groups of 10 connecting Furthermore each links, which in view of the division in tens would have to correspond with 2X5 groups of 20 connecting circuits (Figs. 2 and 2a). If again the traflic with 50 subscribers,

which is handled over the 10 links, is taken to be 3 T. U. (p -0.001), a group of 2000subscribers will supply about 120 T. U., which must also be handled by the 1 2X5 groups of connecting circuits, which, with a some what reduced grade of service or increased blocking chance, is possible and admissible.

, a 'A divisionof the exchange'into 4 groups of 2500,

inclusive of the group of the "0 trafiic, would split up the connecting circuits into 2 4 groups. Each group of 2500 subscribers supplies a'traffic of about 150 T. U., and

then each group of connecting circuits must contain about circuits. With this division, the secondary switches as well as 50 It should be remarked thatif a heavy outgoing traffic over the "0 numbered switches and connections must be expected, it is without further measures possible to increase the number of connecting circuits leading up to the switches which have access to the outgoing lines, to

of Figs. 2 and 2a with the numbers contained in it gives a reasonable decrease of the number of connecting circuits e. a decrease of about half), without the required switching material being inadmissibly increased.

' e. g. 40.or more. It seems that the trnnking'diagram a Figs. 3, 3a, 3b and 3c show a trunking diagram'for a six-digit system. This system must e. 'g. serve a complete mesh-shaped network between a number of exchanges with heavy trafiic, to which other exchanges at the outskirts of this big townnetwork have been connected in a starlike manner. The first digit indicates the star group, the second digit determines the exchange, while the other 'up in accordance with the ideas developed above.

50-point primary (PRIM) and 40-point secondary (SEC) switches in the line-link frame, as is indicated in Figs. 2 and 2a. Y thousand groups each disposing of e. g. circuits.

The connecting circuits are'divided into three groups in accordance with the main routes of the trafiic, i. e.

connecting (1) the group of the local or internal l0,000-unit, (2) the group destined to the other 10,000-units or satellite or minor exchanges ofthe same star-group, and. (3) the group destined to the other star-group centres or exchanges outside the local star-group centre of (1). Such a division of the connecting circuits in three groups, viz. one

smaller group for the internal traffic of the local tenthousand unit, one for the traflic of this ten thousand unit with other star group centres, or other minor exchanges, and one for the traflic of the tenrthousand units with other, dependent or satellite ten thousand units belonging to the same star group centre or minor exchange, is admissible from the point of view of trafiic technique. The outgoing terminals of the connecting 4 .circuit are connected to a switching stage (trunk-link frame I having only secondary switches), which can give through connection to the required 2000 group, of which only. one frame I has been shown in the example. in Fig. 3a. The incoming switches and the outgoing switches of the line-link frame of each 2000 have been multipled in-corresponding groups. The two groups of connecting circuits which lead to the outgoing trunks; both to the higher switching level (other star group centres or minor exchanges) and to the lower switching level (satellite or dependent exchanges of the local star group) are also led via secondary switches of a trunk-link'frame H (see Fig. 3a), in which the outgoing tratfic is distributed over routes to n other star-group centres and m associated satellite exchanges. By way of example 200 outgoing :lines have been provided in total for both switching levels,

which lines can be reached from the local ten'thousand unit.

in principle it is not necessary to discriminate as to the OIlglIl of the incoming lines. As a matter of fact an incoming line from another group centre may have trafiic for the local exchange associated with the group centre;

but this traflic may also be destined for the satellite exchanges 'of this group centre. Then this trafiic is tandem or through traflic to the lower level. It can, however, also -be necessary to apply an indirect or a tandem routing on the level of the group centre. So there must also be a possibility to put through an incoming connection from anexchange of said group to an outgoing trunk to such an exchange.

f It must also be possible to connect through the trunks coming-in from the satellite exchangeswith the three main possibilities described before. To this end the switching diagram of Fi'gs. 3b and 3c offers the following possibilities. Each incoming trunk (in the example -2 400 lines) is connected e. g. to an arc ofaZO-point switch, twenty of which are multipledtogether. Twenty of these groups of primary switches FRIM of the incom ing trunk-link frameare connected to secondary switches SEChav ing an equal number of positions, together giving access to 400 outlets, in a conventional manner known.

On these secondary switches SEC the trafilc is disincoming lines The subscribers have been divided into 5 twochances tributed over 5 local 2000-groups (Fig. 3d) and the various group centres or minor exchanges and satellite or dependent exchanges (Fig. 3b). If :he number of each of these groups is not too large (5 to 6), it is not necessary to provide a following switching stage. Apparently it is recommenda'ble not to couple the outgoing (or transit) lines of the tandem exchange with the outgoing lines of the local exchange. In doing so markets can be used more or less freely, using separate markers for local originating traflic and for through traflic.

If the staror group centre contains more than two or three local 10,000-units, it may be necessary to insert a half link-frame such as frame I or II in Fig. 3a comprising only secondary switches, between the secondary switches of the trunk-link frame of the incoming lines.

'Fig. 4 symbolically shows the trunking diagram of a group centre or minor exchanges with a dependent or satellite exchange connected to it. The trunking diagram of Figs. 2 and 2a (omitting the switch between the outgoing side of the connecting circuit and the outgoing lines) has been represented together with the diagram of Figs. 3, 3a, 3b and 3c symbolically in Fig. 4. The satellite or dependent exchange has internal trafiic via a line-link frame consisting of primary and secondary switches. The outgoing trafiic passes onlytone link-frame, which is admissible with heavy traffic in the direction of the minor exchange or star-group centre, which as a rule is the case in such an exchange. H

With the given switches the incoming traffic must be handled via two trunk link-frames each comprising a primary and a secondary switching stage. Registers can be connected in the usual manner.

For the internal trafiic the star-group centre or minor exchange contains one switching more than the satellite or dependent exchange, i. e. secondary switching stage S in the trunk-l nk frame. For reasons of uniformity (i. e. in view of the incoming and the out going lines) the connecting. circuit in this figure has been split up into two half connecting circuits. At the top of Fig. 4 the functions with other group centres or minor exchanges have been shown, at the bottom of the figure those with the indicated and other satellite or dependent exchanges, if any. They always contain an incoming or an outgoing half of a connecting circuit.

The registers can again be connected on in the usual manner.

The connections 11 and 12 which have a vertical course in the secondary trunk-link frame indicate the trafiic that is handled in tandem, i. e. trafiic originating from satellite exchanges and group centres which is destined for other satellite or dependent exchanges or group centres or minor exchanges.

Fig. 5 shows the principle of the positioning of the crossbar switches in a system according to the trunking diagram of Figs. 2 and 2a.

Fig. 5 shows a number of bridges of crossbar switches the primary and secondary stages of the line-link frame. Between the primary and secondary switches of the lineliuk frame of a group of 2000 subscribers there are 400 links which in groups of 40 go to 10 groups of e. g. 10 secondary switches SEC for the outgoing trafiic, and 10 groups of e. g. 10 secondary switches for the incoming traflic. For each of the 10 groups of secondary switches (bridges) which have been assembled in a number of crossbar switches, a control circuit C has been provided.

So per 2000 subscribers with 100 connecting circuits there are 10 control circuits C. The primary switches PRIM belonging to this group of 2000 subscribers can likewise be subdivided. into 10 groups, each of which co-operates means of the same control circuit C as the co-opei'ating group of secondary switches. V

This means that if such a control circuit 'C breaks down, only one tenth of the trafiie of a group of 2000 subscribers 'is affected, because one control circuit is provided 'for each corresponding n multiple of links multipied over all of the link groups, i. e. the first links of each group are multipled to one control circuit C, the second'to another control circuit, etc.

A calling subscriber gets access to a sender or register REG in a manner as usual in the crossbar systems. As this operation is in no way connected with the invention .it need not be described further here. The sender (REG) sends dialling .tone to the calling subscriber, who dials the four digits, after which the positioning of the required connection is started. E. g. for a group of .2000 subscribers a maximum of 20 senders is provided, which in their turn dispose of a maximum of 5 markers of asimple construction (see Carpenter U. S. Patent No. 2,093,117, issued September 14, 1937). So when a sender has received the four digits, it seizes a .free marker, to which the whole number of the subschiber to be called, as well as the number of the calling subscriber (which is comr'nun'icated to the sender in the manner usual for crossbar systems) is transmitted.

The switch MSA belonging individually to a marker and preferably consisting of .a number of bridges of a crossbar switch, has 40 positions and 10 wipers by means or" which access can be had to the engaged indications of all the links bet-Ween the primary switches and the secondary switches of the line-link frame belonging to the relevant group of 2000 subscribers. Under the control of the called subscribers number, the switch MSA is set into that position in which the 10 engaged indications of the links serving the group of subscribers in which the calling subscriber occurs, are connected to the marker. At the same time the switch MSB which can also be a partof a crossbar switch and which has e. g. 5 X5 posi fions (5 positions corresponding with-each group of 200!) subscribers), is positioned under the control of the called subscriberis number. Each of the 5 positions of this switch MSB belonging to one group, gives access to a switch, such as MSA, giving access to the engaged indications of all the links between the primary and 'th6;sec onda-ry switches ofthe 2000 unit. So 5 di-tferent-markers out of the whole group of markers can survey the engaged position of the links in a 2000 unit. The group of 1!) connecting links via which the connection can be set up, are connected to the marker. Furthermore aconnection is established via switch MSe between the marker and the-engaged indications of the connecting circuits. switch has 5 positions and 20 wipers. .The fact is that there is always a group of 20 connecting circuits via which the required connection can beset up. The marker makes a selection among the three groups of 10' (incoming links), 20 (connecting circuits), and 10 (outgoing links) possibilities of making the connection respectively. As a matter of fact this selection is restricted to three free links, which are mutually reachable oravailable.

Provided the suitable switching means are used, such a selection can be made by a number of markers simultaneously in the same groups of links. The engaged indications of the links between the primary and secondary switches can be so arranged that only those can be selected in which the corresponding control circuit C is free, and that the seizure of a- .link implies the seizure of this control circuit. Such a switching method is known from the normal automatic switching systems such as e. g. the Antwerp, Belgium Bell Telephone 7 D Rotary system.

'In principle the device for selecting together the route through the exchange, towhich route consists of three tobe called. V v r If many wires are'available between marker and con- "trol circuit, the control circuits need in principle only contain the magnets of the crossbar switches to be op- This number of wires can be restricted appreciably by the use of some relays in the control circuits 'C and C, such as shown in Oberman copending 'applica:

marker with the difierent switching stages. 6a are an elaboration of Fig. 5. also representing an in- The trunking device will not be described further. The testing device in a the marker, for testing groups of links and taking the free 'nth one from each group, shows which of the 10, 20, 1O connecting links, respectively, are seized or will be used for the connection to be set up. The marker sets the switch .MSD in the position corresponding with the control circuit C belonging to the switches of the line-link frame that correspond with the selected link. Furthermore the switch'MSn is positioned on the control circuit C' ofthe selected two-thousand group, which controls'the switches that operate the selected link. The control circuits C and C can be connected without further measures because by the selection of the links they had already been safeguarded from being seized by other markers.

I'NeXt the marker gives on the calling and the called sides, respectively, the required control information to the primary and secondary switches ofthe line-link frame.

' From the control circuit and the positioned selecting stages the marker can be connected to the line of the subscriber to .be called to make the free test, if ithad not already been efiected via paths outside the selecting tion at the calling subscribers line circuit and to send him busy tone from that circuit. If the called subscriber is free, the speech path is switchedthrough via the connecting circuit, ringing tone being sent to the subscriber erated.

tion Serial No. 316,573, filed October 24, 1952.

. The switching structure designed is not yet complete because the subscribers numbers disposing of more'tban one line cannot be dealt with in this manner. The fact is that the access to the next line of such a subscribers number, which preferably must be established in another 50 in view of the distribution of the traffic (particularly if no non-decimal system combined with conversion is applied, as has been designed in the crossbar systems of the Western Electric'CoJ, may have to be gained via quite another route through the exchange, therefore it will not be sufl'icient to operate switches in the speech route repeatedly. I

It will therefore be necessary to add a device such as shown in the above mentioned Carpenter patent or in.

Obermans copending application .Serial No. 230,277,

filed June'7, 1951, to the marker for testing auxiliary lines,so that the marker before positioning a connection ascertains which line will be taken. To maintain the simplicity of the system and in view of the space available in the crossbar switches, it will be assumed that 20% offtheavailable numbering capacity can be adapted to group-numbers. 7

Figs. 6 and 6a show by way of example the trunking diagram of an exchange for 2000 lines with a diagrammaticview of the coupling of a sender REG and a Figs. 6 and dependent exchange with 10,000 lines. diagram of Figs. 6 and 6a has a trunk-link frame for the traflic to the two ten-thousand units. Such a frame, however, is not strictly necessary.

the switches of the trunk-link frame in Fig. 6a have been drawn as selectors enclosed in the dashed line rectangles between parallel vertical dashed lines outlining the frame,

itself, in contradistinction to those of the trunk-link frame in the local part of the switching diagram of Fig. 3a.

To indicate that the' applied symbols representing selectors or finders can always be interchanged in systems with crossbar switches,

, r The marker can test by means of the switch MSA the engaged condition'sof all the links which the calling subscrib'er has at his disposal, the link via which the connection with the called subscriber will be established being tested via the switch MSB (arc b) and one of the switches MSG- The'connecting circuits via which the 7 connection will be set up and the one of the trunk links are tested via the switches MSn and MS13 (are a), respectively. Now the marker must select together four successive free and mutually reachable links. Via the switch MSn the positioning information is given to the control; circuit operating the switches in the line-link frame via which go the designated links. .Via MSr', arcs a and b, the information regarding the designated trunk-link and the required positioning of the line-link frame for the subscriber to be called is transmitted to the relevent' con-' trol circuits. In Figs; 6 and 6a the crossbar switch bridges allotted to one control circuit have been surrounded with a dashed line IV or IV.

While I have illustrated and described what I regard to incoming stages, outgoing link circuits between said out- 7 going stages, connecting circuits between said incoming and said outgoing stages, and senders associated with said incoming stages; the improvement comprising: a plurality of markers, means for connecting a sender toa calling terminal, means for connecting said sender to a marker,

means controlled by said marker for selecting a free in- 7 coming link circuit, a free outgoing link circuit and a mutually available free connecting circuit between said free linkcircuits all of which three circuits are connectable in series between said calling and said called terminals, control circuits connected with said link circuits, means for connecting a said control circuit connected with each reserving said control circuits connected with said selected.

free link circuits until they are connected to said marker.

4. A system according to claim 1 whereinsaid means for setting up said connection sets it up simultaneously through said selected link and connecting circuits.

5. A system accordingto claim 1 including means for connecting said marker to said called terminal to test the free condition of said terminal. a V

6. A system according to claim 1 wherein said means for selecting said free link and connecting circuits includes a by-path circuit through said system separate from said connection through said selected fiee link and connecting circuits. I g

7. A system according to claim 1 wherein said selecting stages are composed of groups of selector switches.

8. A system according to claim 7 wherein said selector switches are crossbar switches.

9. A system according to claim 7 wherein said means for setting up said connection includes means for posi-' tioning, said selector switches connected to said selected link and connecting circuits. 1

10. In an automatic switching system between a plurality of subscribers terminals wherein any one subar ing-ass 9 scrib'ers terminal can be connected to any other subecriberis terminal in the system, said terminals each having a corresponding call signal whereby a calling sub- '-scriber-can automatically be connected to a called subscriber by transmitting the call signal corresponding to said called subscriber to said system, said system having at least two incoming and two outgoing selecting stages of groups of selector switches, first groups of link circuits between the selector switches of said incoming selecting stages, second groups of link circuits between the selector switches of said outgoing selecting stages, connecting-eircuits betwcen the selectorswitches of said incoming and outgoing stages, and senders associated with-said incoming stages; the improvement comprising: a plurality of markers connectable to any of said link and connecting circuits and senders, means for connecting a sender seized by a calling subscribers terminal to a free marker,

means controlled by said marker for connecting said marker to a free link circuit of said first groups, a free second link circuit of said second groups and a mutually available free cord circuit between said'free link circuits,

of which free circuits are connectable in series hetween said calling and said called subscribers terminals,

control circuits connected with groups of said link circuits, means for reserving a free control circuit connected with each said selected link circuit, means for connecting said reserved control circuits to said marker, means controlled by said control circuits for simultaneously positioningthe selector switches connected tosaid selected link and connecting circuits for setting up the connection through said link and connecting circuits between said :callingtand said called subscribers terminals.

ll. In an automatic electrical switching system between a plurality of subscribers terminals wherein any one subscribers terminal .can be connected to any other subscribers terminal in the system, said terminals each having a corresponding call signal whereby a calling subscriber can automatically be connected to a called subscriber by transmitting the call signal corresponding to said called subscriber to said system, said system having 1 at least two incoming and two outgoing selecting stages of groups of selector switches, incoming link circuits between the selector switches of said incoming selecting stages, outgoing link circuits between the selector switches of said outgoing selecting stages, connecting circuits between the selector switches of said incoming and outgoing stages, and senders connectable with said incoming stages; the improvement comprising: a plurality of markers connectable to any of said link and connecting circuits and senders, means for connecting a sender seized by a calling subscribers terminal to a free marker, means for transmitting the called terminals signals to said sender and then to said free marker to control said marker, separate by-path means controlled by said marker for simultaneously connecting said marker to a free incoming link circuit, a free outgoing link circuit and a mutually available free connecting circuit between said free link circuits, all of which free circuits are connectable in series between said calling and said called subscribers terminals, control circuits connected with said link circuits, means for reserving and busying a free control circuit connected with each said selected link circuit, means for connecting said reserved control circuits to said marker, means controlled by said control circuits and said marker simultaneously positioning the selector switches connected to said selected link and connecting circuits for setting up the connection between said calling and said called subscribers terminals, and means for connecting said marker to said called terminal to test its free condition.

12. In an automatic switching system for a plurality of subscribers where any one subscriber can be connected to any other subscriber in the system, said system comprising: a subscribers link frame having at least a primary selecting stage of selector switches and a secondary selecting stage having incoming and outgoing selector switches,

connecting circuits between said incoming and outgoing secondary selecting stage switches, incoming and outgoing link circuits 'between said primary and secondary stage switches, first means for directly connecting the subscribers to said primary stage switches, one of a plurality of markers connected to each of said incoming and outgoing links and connecting circuits for determining which incoming link, outgoing link and connecting circuit are free and connectable in series between a desired calling and called subscriber, separate control circuits for 'said incoming and outgoing links for positioning the switches of said stages, and means responsive to said first means for selecting separate corresponding control circuits for the 'free incoming and outgoing link circuits to position simultaneously the switches of the stages connected "to said free links and connecting circuit which are connectable in series between said calling and said called subscribers.

13. In an automatic switching system between a plurality of subscribers lines, any one of which canbe connected to any other subscribers line in the system, said system including a primary and a secondary switching stage, each of which stages has ap'lurality of multi-contact switches, the improvement comprising: line groups into which said subscribers lines are arranged, distinct :groups of a plurality of multipled switches in each switching stage of each line group, each subscribers line being multipled to the switches in one group of said primary switching stage, and cross-bar switches connected to form another groups comprising the multipled switches of said secondary switching stage and one of the switches of each of the groups in said primary switching stage, whereby each subscribers line is connectable to a plurality of said crossbar switches.

14. A system according to claim 13 including a control circuit for each of said cross-bar switches in said other group connecting the multipled switches of each group in said secondary switching stage with a multipled switch from each group in said primary switching stage.

15. A system according to claim 14 including a plurality of marker circuits for each line group, finder switches for connecting said marker circuits to each group, and other finder switches for connecting said marker circuits to said control circuits, whereby all of the switching stages between two given subscribers lines may be set-up simul taneously under the control of said marker and control circuits.

16. A system according to claim 15 including busy test contact connections between said switching stages and said marker circuits.

17. A system according to claim 13 having finding and selecting primary and secondary switching stages.

18. A system according to claim 17 including a plurality of senders connectible to each group of said finding secondary switching stage.

19. A system according to claim 17 including connecting circuits conncctible between the finding switching stages to the selecting switching stages.

20. An automatic switching system having a plurality of terminals any one of which can be connected to any other thereof, said system comprising: primary and secondary finding and selecting switching stages between any two of said terminals, a plurality of multi-contact switches in each stage, said terminals being arranged in terminal groups and said multi-contact switches being multipled into groups associated with each said terminal group, means for connecting each said secondary stage group of a given terminal group to a multi-control switch from each said primary stage group of the same given terminal group to form a connected group of switches, separate control circuits connected to each finding and to each selecting connected group of switches, a register connectable to each said connected group of switches, and a marker circuit connectable to said finding and said selecting control circuits by means of which control circuits the establish- 1118111 of a connection between two terminals may be set up outside said switching stages whereby each terminal has available more than one connection to reach a free vregister and a free marker circuit.

tSWitCh having both primary and secondary switching stage sections. 7 V

23. An automatic switching system having a plurality of subscribers each having a subscribers set, any one or or called subscriber through an exchange, said system comprising: primary and secondary finding and selecting switching stages between a calling and called subscribers set, a plurality of multi-contact switches in each said stage,

said subscribers set being divided into firstgroups, said ,multi-contact switches in each primary switching stage beingmultipled into second groups of switches within 7 each said first group, said rnulti-contactswitches in each a a fourth group of interconnected switches, separate control circuits connected to each said fourth group of interconnected switches in both said finding and said selecting stages, a plurality of senders each being connectable to a said fourth group of connected switches in said'finding stages of each said first group, and a plurality of marker circuits each being connectable to botha said finding and subscribers. 7

calling subscriber of which can be connected to any other .finder switches connected with each marker circuit for a said selecting control circuit by means of which the establishment of a connectionbetween a calling and a ,called'subscribers set may beset up outside said switching stages for selecting simultaneously free and available finding and selecting stage switches for connecting said 24. A system according to claim 23 wherein said marker circuits include means for busy testing said second and third groups of switches of both'said finding and said selecting switching stages.

25. A system according to claim 23 wherein each said fourth group of interconnected switches comprises cross- ,bar type of switches in both-primary and secondary switching stagesections.

26. A system according to claim 23 including marker connecting said marker circuits totheir corresponding control circuits. 7

27. A system according to claim 23 wherein said third group of switches of said finding and said selecting stages areinterconnected by means of connecting circuits.

' 28. A system according to claim 27 including market finder switchesv connected with each marker circuit for connecting said marker circuits to said connecting circuits.

References Cited inthefile of this patent UNITED STATES PATENTS Gillings et a1; Dec. 10, 1946 2,582,959 Bruce et al Ian. 22, 1952 r 2,583,848 Johnson Ian. 29, 1952 2,598,412 Modee et a1. May 27, 1952 Ostline Mar; 10, 1953 

